(1) Field of the Invention
This invention relates to the packaging of rolled webs of light sensitive material e.g. strips of photographic film or paper for loading into a camera or other apparatus in which the material is to be exposed.
Such rolls are often packaged in light tight lidded containers from which the roll must be removed preparatory to loading it into the exposure apparatus and there is a risk of the material being spoiled by environmental light unless this loading is carried out under safelight conditions.
(2) Summary of Prior Art
Various proposals have been made in order to avoid such spoiling risks, and thus allow roomlight loading of the roll. Examples of such proposals are described in U.S. Pat. Nos. 4,148,395 and 4,505,387, and Research Disclosure May 1983, No 22932 page 190 and European Patent Application published under Nos 0 181 417 A1.
Each of these proposals suffers from certain disadvantages in the mass production of packaged rolls. It will be appreciated that the width of the rolled web is controlled during manufacture within quite close tolerances, so the axial length of the roll is also well-defined. Of course webs of various different standard widths may be manufactured. A principal cause of the packaging problems encountered lies in variations in the overall diameter of the rolled web. For a given standard length of the web material the overall diameter of the rolled web can vary quite markedly: a common standard rolled web has a nominal diameter of 113 mm, but in practice, deviations of as much as 2 mm from this nominal diameter may be encountered. These deviations can be attributed to quite small variations in the thickness of the web support or of any coatings on the web as between one roll and another, and it will appreciated that these variations must be multiplied by the number of convolutions with which the webs are wound to form the rolls.
U.S. Pat. No. 4,148,395 proposes to overcome the problem of roomlight loading by providing a rolled web with an exterior length of opaque leader. The web is rolled onto a core and the ends of the roll are protected against light by oversized annular end covers which are adhered to the ends of the core. The outer margins of the end covers are radially slit to form tabs which are also coated with adhesive so that they can be folded down onto the outer convolution of the leader to form with the leader a light tight package. An end portion of the leader is of less width than the remainder so that it is free of the end cover tabs and can be used to tear the remainder of the leader away from the end covers after roomlight loading into a cassette or directly into the exposure apparatus. The radial slits extend inwardly of the end covers, but not as far as the nominal overall diameter of the rolled web. If however the roll being packaged is oversized, there is a risk that light would be able to penetrate through those portions of the slits which cannot be folded over onto the leader. If on the other hand the rolled web is undersized, folding the margins of the end covers over the leader is likely to cause buckling and there is a risk that light may penetrate through such buckles. A further problem arises in that the annular end covers must be accurately registered with the core so that their inner margins can be reliably and light tightly sealed to the ends of the core. Furthermore, such cores are in practice often made of cardboard, and it is often difficult to ensure a reliable light tight seal to the end face of a cut cardboard roll core.
In U.S. Pat. No. 4,505,387, a slightly different approach is adopted. Annular end covers are made corresponding to the nominal overall diameter of the rolled web, and a circumferential wrapping sheet is adhered to the leader convolution. The wrapping sheet is wider than the leader and rolled web, and its margins are slit, but not inwardly as far as the edges of the leader, to form tabs which are folded down and adhered to the end covers whose inner margins are adhesively bonded to the ends of the core on which the web is wound. Such a wrapping depends for its light tightness on an accurate positioning of the wrapping sheet on the leader, and again there is a risk of light penetration at the periphery of each end cover if a rolled web has an overall diameter greater than nominal. Again, accurate registration of the annular end covers and the core is necessary to achieve proper and reliable sealing so as to avoid the ingress of light.
Research Disclosure No. 22932 shows an arrangement in which annular end covers are each attached to an opaque leader by a tape. This arrangement requires rather accurate positioning of the tapes and end covers, and it is not a particularly satisfactory solution of the problem of preventing light penetration at the periphery of the end covers of an oversized rolled web.
Our European Patent Publication No 0 181 417 A1 proposes rolling an overwidth sheet of material with the web leader to form a tube longer than the rolled web and heat shrinking that rolled tube so that its projecting end portions collapse inwardly against the end faces of the roll. We have presently abandoned this proposal for various reasons. Inter alia, the requirement for heat shrinkability rules out the use of certain wrapping materials which we would prefer to use because of their benefits in light, air and moisture tightness, and the shrinking causes stresses at the edges of the roll which can cause deformation of the leader or pressure fogging of the light sensitive material, or undesirable weakening or even rupture of the wrapping material at that location.